Search PubMed⌕ Search

Biomedical subjects

A Barth

Publications and source records attributed to A Barth.

At least 163 records · Page 9Linked to original sources
PubMed1989

Reactions between dipeptidyl peptidase IV and diacyl hydroxylamines: mechanistic investigations.

Kinetics of inactivation of dipeptidyl peptidase IV (DP IV, EC 3.4.14.5) by N-peptidyl-O-(4-nitrobenzoyl) hydroxylamines and their enzyme-catalyzed hydrolysis were followed using independent monitoring methods, all giving similar efficiency ratios of Kcat/Kinact. Different temperature dependences of the DP IV-inactivation and enzyme-catalyzed hydrolysis provide evidence of independent rate determining steps for both reactions. Activation parameters of inactivation are similar to those of spontaneous decomposition of the compounds, suggesting a mechanistic relationship. Investigation of DP IV-inactivation, DP IV-catalyzed hydrolysis of N-Ala-Pro-O-Bz(4-NO2) and the decomposition of the suicide substrate in H2O and D2O gave solvent isotope effects of 4.65, 2.54 and 1.02, respectively. A proton inventory of the inactivation reaction indicates involvement of more than one proton in the formation or breakdown of its transition state. The linear proton inventory found for the hydrolytic reaction is consistent with one proton transition in the rate determining step and resembles the rate limiting deacylation of Ala-Pro-DP IV. The hypothetical reaction model now locates splitting in both reactions prior to formation of a covalent intermediate during the catalytic cycle.

Dipeptidyl Peptidase 4↗
PubMed1989

[Application of dipeptidylpeptidase IV in formation of the peptide bond].

According to the increasing importance of enzyme catalysed peptide synthesis the capability of the protease dipeptidyl peptidase IV is shown to form the peptide bond. To our best knowledge, it's the first time that has been used successfully proline as one of the amino acids. The formation of the peptide bond is kinetically controlled. Free amino acids have been used as nucleophiles. The reaction media contain 50 vol.-% glycerol. A first approach to a kinetic treatment is shown.

Amino Acid Sequence↗
PubMed1988

[Wound infection following appendectomy. Metronidazole vs ornidazole as single-dose prophylaxis in non-perforated appendix].

In an open prospective randomized study, the postoperative wound infection rate following removal of an unperforated appendix was evaluated in 187 patients who received either metronidazole (1 g suppositories) or ornidazole (500 mg iv or 500 mg suppositories) in a single dose preoperatively. The overall postoperative infection rate was 2.1%. Metronidazole and ornidazole suppositories are a cheap method of preventing postoperative infection in cases of unperforated appendix.

Adolescent↗
PubMed1988

Mechanism of proline-specific proteinases: (I) Substrate specificity of dipeptidyl peptidase IV from pig kidney and proline-specific endopeptidase from Flavobacterium meningosepticum.

The substrate specificity of dipeptidyl peptidase IV (dipeptidyl peptide hydrolase, EC 3.4.14.5) from pig kidney and proline-specific endopeptidase from Flavobacterium meningosepticum, was investigated with a series of N-terminal unprotected (dipeptidyl peptidases IV) and succinylated dipeptidyl-p-nitroanilides (proline-specific endopeptidase). Both enzymes are specific for the S configuration of the amino-acid residue in P1 and P2 position if the penultimate residue is proline. In the case of alanine substrates (Ala in P1, dipeptidyl peptidase IV hydrolyzes such compounds where the configuration of the P2 residue is R. The penultimate residue with dipeptidyl peptidase IV can be, beside proline and alanine, dehydroproline, hydroxyproline and pipecolic acid. Proline substrates (Pro in P1) with an R configuration in P2 are inhibitors of the hydrolysis of proline substrates with an S,S configuration in an uncompetitive (dipeptidyl peptide IV) or mixed inhibition type (proline-specific endopeptidase). Derivatives of Gly-Pro-pNA where the N-terminal amino group is methylated are hydrolyzed by dipeptidyl peptidase IV.

Amino Acid Sequence↗
PubMed1988

Are Z-Arg-Gly-Phe-Phe-Leu-MNA and Z-Arg-Gly-Phe-Phe-Pro-MNA suitable substrates for the demonstration of cathepsin D activity?

The suitability of Z-Arg-Gly-Phe-Phe-Leu-MNA and Z-Arg-Gly-Phe-Phe-Pro-MNA for the assessment of cathepsin D activity was tested in biochemical and histochemical experiments. Substrates were dissolved in dimethylformamide and used at 0.1-0.5 mM in various buffers over a pH range of 3.5-7.4. Homogenates of various rat organs and isolated purified enzymes [cathepsin D from bovine spleen, dipeptidyl peptidase (DPP) IV from porcine kidney and rat lung] were used as enzyme sources. Pepstatin, di-isopropylfluorophosphate (DFP), p-chloromercuribenzoate, o-phenanthroline and a series of DPP IV inhibitors were used in inhibitor experiments. At pH 3.5 and 5.0, substrates were used in a two-step postcoupling procedure with aminopeptidase M and dipeptidyl peptidase IV as auxiliary enzymes and Fast Blue BB as coupling agent. Results were compared with those obtained with haemoglobin. Above pH 5.0 substrates were used in a one-step postcoupling procedure. Cryostat sections of snap-frozen or cold aldehyde-fixed tissue pieces of various rat organs and biopsies of human jejunal mucosa were used in histochemical experiments. As in biochemical tests a two-step procedure was used in the pH range 3.5-5.0, but Fast Blue B was used in the second step for the simultaneous coupling. Above pH 5.0 a one-step simultaneous azo coupling procedure was used with Fast Blue B as coupling agent. At pH 3.5 the hydrolysis rate of both synthetic substrates was about 100x lower than that of haemoglobin when cathepsin D from bovine spleen was used.(ABSTRACT TRUNCATED AT 250 WORDS)

2-Naphthylamine↗
PubMed1988

Infradian biorhythms of enzymuria in man?

The temporal courses of dipeptidyl peptidase IV gamma-glutamyltransferase and alanine aminopeptidase were followed over 70 days in the morning urine of 15 healthy persons. Subsequent to basic statistical analysis a two-step procedure was performed, including spectral analysis and the fit of a cosine function by non-linear regression. The excretion of the 3 enzymes followed an infradian biorhythm with a mean period length of 10.04 for dipeptidyl peptidase IV, 13.34 for gamma-glutamyltransferase and 10.17 for alanine aminopeptidase. In addition to the basic rhythmic process described by the fitted cosine functions, in most of the enzyme patterns steap peaks of very high excretory activity appeared which was verified in repeated measurements. These infradian biorhythms with changes in the range of 100% and more, as well as their interindividual variations, have to be considered in assessing the excretion of enzymes.

Adult↗
PubMed1988

Dipeptidylpeptidase IV--inactivation with N-peptidyl-O-aroyl hydroxylamines.

Eleven N-peptidyl-O-aroyl hydroxylamines have been synthesized and their hydrolytic stability, acidity and properties during reaction with dipeptidyl peptidase IV (E.C. 3.4.14.5) investigated. N-peptidyl-O-(4-nitrobenzoyl) hydroxylamines act as irreversible inhibitors of serine proteases. The serine enzyme, dipeptidyl peptidase IV (DP IV), is inactivated by substrate analog derivatives of this class by a suicide inactivation mechanism. During the enzyme reaction of DP IV with the suicide substrates most molecules are hydrolyzed but some irreversibly inactivate the target enzyme. In contrast to porcine pancreatic elastase and thermitase, DP IV exhibits a high ratio for hydrolysis of the compounds versus inhibition during their interaction with the enzyme. Variation of the leaving aroyl residue lowers this ratio. Variation of the substrate analog peptide moieties of the DP IV-inhibitors increases their ability to inhibit the enzyme to a remarkable extent. Possible reaction pathways are discussed.

Dipeptides↗
PubMed1988

Molecular interactions in intermediate and transition states in the self-stimulated inhibition of enzymes.

Di-isopropyl fluorophosphate (DFP) and other organophosphorus inhibitors recruit the catalytic power of their target enzymes: the enzyme catalyzes its own irreversible phosphorylation. The magnitude of the catalytic acceleration can approach the factor by which the enzyme catalyzes its own acylation by natural substrates. The reaction of DFP with five serine proteases [chymotrypsin, elastase, dipeptidyl peptidase IV (DP IV), subtilisin and thermitase] exhibits in all cases the same pH dependence as does enzyme acylation by natural substrates. Chymotrypsin and elastase form a "fast" class of enzymes which react about ten-fold faster than the other three "slow" enzymes. All enzymes show k(HOH)/k(DOD) of about 2 but the proton inventory indicates one-proton character for "slow" enzymes and multiproton character for "fast" enzymes. Enthalpies of activation are about 33 kJ/mol (subtilisin, "slow") and 10 kJ/mol (elastase, "fast"). Entropies of activation are about -120 J.T-1.mol-1 (subtilisin, "slow") and -175J.T-1.s-1 (elastase, "fast"; T = temperature in K).

Enzyme Inhibitors↗
PubMed1988

Circulatory activity of dopamine-dipeptide compounds.

Three newly synthesized dopamine-dipeptide compounds (Gly-Pro-dopamide, Lys-Pro-dopamide, Z-Lys-Pro-dopamide) which should be cleft in vivo by the enzyme dipeptidyl peptidase IV (EC 3.4.14.5) were investigated as to their protective activity against hemorrhagic shock in rats. All three compounds increased significantly the survival times of animals, subjected to hemorrhage, in nearly the same manner as dopamine did. They also relaxed the blood vessels of isolated perfused rat kidneys pretreated with phenoxybenzamine. This activity demonstrates a vasodilation via dopaminergic receptors. Regarding the blood pressure increasing activity, mediated by excitation of alpha-receptors, Gly-Pro-dopamide was less potent than dopamine but affected blood pressure about four times longer than dopamine did. Lys-Pro-dopamide and Z-Lys-Pro-dopamide were nearly equieffective to dopamine.

Animals↗
PubMed1988

Effects of beta-casomorphin in isolated heart preparations.

beta-Casomorphin-5, a novel opioid peptide Tyr-Pro-Phe-Pro-Gly, was tested in isolated heart preparations of guinea pigs in comparison with other morphine related peptides and cardioactive drugs. The substance induced a dose-dependent change in the cardiac contraction force, showing a positive inotropic effect in low concentrations (10(-9) - 10(-7) mol/l) but a cardiodepressive action at higher doses (10(-7) - 10(-5) mol/l). Similarly, potentiation phenomena due to varied pacing rates of right-ventricular strips were enhanced at 10(-8) mol/l and lowered at 10(-6) mol/l beta-casomorphin-5. The coronary flow continuously increased. The observed changes of heart action were not mediated by opioid receptors: specifically acting opioid peptides were without influence and naloxone had no inhibitory effect. Peptides with similar sequences may exert a regulatory role in cardiac function, possibly mediated by an influence on the cellular calcium fluxes. The results may prove to be useful for the detection and estimation of more stable and cardioactive peptides.

Animals↗
PubMed1987

[New aspects in the surgical treatment of hyperparathyroidism].

As a result of routine serum calcium determinations an increasing number of primary hyperparathyroidism (pHPT) cases are detected. While surgical treatment of the symptomatic patient with pHPT is generally accepted, this may not be the case in asymptomatic and especially elderly patients. The value of preoperative localization of parathyroid tumors has not been clearly established. In our experience dual parathyroid imaging with thallium and technetium has provided the best results. With the growing number of dialyzed patients, secondary (sHPT) and tertiary hyperparathyroidism (tHPT) are assuming increasing importance. Patients suffering from symptomatic sHPT or tHPT should undergo parathyroid surgery. After respective follow-up of 3.8 years (pHPT) and 2 years (sHPT and tHPT), all the cases with pHPT showed a relevant fall in serum calcium levels and PTH.

Biopsy↗
PubMed1987

The role of dipeptidyl peptidase IV in human T lymphocyte activation. Inhibitors and antibodies against dipeptidyl peptidase IV suppress lymphocyte proliferation and immunoglobulin synthesis in vitro.

Dipeptidyl peptidase IV (DP IV), an ectoenzyme in the cell membrane of T lymphocytes, is an important constituent in the process of lymphocyte activation. This conclusion is drawn from the following observations: (a) Proliferation of peripheral blood lymphocytes induced by mitogenic lectins (phytohemagglutinin, concanavalin A, pokeweed mitogen) is suppressed in the presence of DP IV inhibitors. This effect is specific and applies to an irreversible suicide inhibitor as well as to a competitive one in a dose-dependent fashion. (b) Inhibition of DNA synthesis was also induced by a polyclonal anti-DP IV immunoglobulin. (c) As a consequence of impaired T cell function the production of immunoglobulins by pokeweed mitogen-stimulated lymphocytes is also markedly reduced in the presence of DP IV inhibitors.

Antibody Formation↗
PubMed1987

Influence of triiodothyronine and dexamethasone on the postnatal development of hepatic eosine transport in rats.

In male Wistar rats of different ages the influence of a three days pretreatment with triiodothyronine (T3, 100 micrograms/kg b.m.s.c.) or dexamethasone (0.4 mg/kg b.m.i.p.) on eosine accumulation of rat liver in vitro and biliary excretion of eosine in vivo was investigated. T3 stimulated the eosine accumulation in liver slices. This in vitro effect was not paralleled by higher serum elimination rates of eosine in vivo. Neither T3 nor dexamethasone could accelerate the maturation of the rate limiting excretion process for organic anions in developing rats.

Age Factors↗
PubMed1987

Role of dipeptidyl peptidase IV in uptake of peptide nitrogen from beta-casomorphin in rabbit renal BBMV.

We examined the handling of radiolabeled beta-casomorphin, Tyr-Pro-[3H]Phe-Pro-Gly, by rabbit renal brush-border membrane vesicles (BBMV). The uptake of radiolabel into the vesicles was Na+-independent, but an inward-directed H+ gradient stimulated the uptake. The H+ gradient-dependent uptake was further accelerated by an interior-negative membrane potential, but inhibited in the presence of a protonophore. Treatment of the membrane vesicles with diisopropylfluorophosphate (DFP) greatly reduced the uptake of the radiolabel. Control as well as DFP-treated vesicles exhibited H+ gradient-dependent Gly-Sar uptake. Unlabeled beta-casomorphin inhibited Gly-Sar uptake in control vesicles, but the inhibition was significantly reduced in DFP-treated vesicles. DFP inhibited the activity of dipeptidyl peptidase IV in these vesicles and there was a direct correlation between the activity of the enzyme and the capacity of beta-casomorphin to inhibit Gly-Sar uptake. Many di- and tripeptides reduced the uptake of Gly-Sar and the uptake of radiolabel from beta-[3H]casomorphin to a similar extent. We conclude that beta-casomorphin is hydrolyzed by dipeptidyl peptidase IV and the products are transported into the vesicles by the H+ gradient-driven peptide transport system. This conclusion is supported by the results from the analysis of the incubation medium by high-performance liquid chromatography that showed rapid hydrolysis of the pentapeptide by brush-border membranes to di- and tripeptides.

Animals↗
PubMed1987

Stepwise degradation of the hexapeptide Met-Ala-Ser-Pro-Phe-Ala by dipeptidyl peptidase IV.

Dipeptidyl peptidase IV (dipeptidyl-peptide hydrolase, EC 3.4.14.-) purified from pig kidney was proved to split off the N-terminal dipeptide Met1-Ala2 and, subsequently the dipeptide Ser3-Pro4 from the synthetic model peptide Met-Ala-Ser-Pro-Phe-Ala representing the N-terminal part of a signal sequence of leucocyte interferon. The kinetic parameters for the release of Met1-Ala2 (Km 3.2.10(-5) mol.l-1 and Ser3-Pro4 (Km 1.65.10(-4) mol.l-1, kcat57.9 s-1) were determined. The dipeptides Ser-Pro and Phe-Ala were found to be competitive inhibitors of the hydrolysis of Gly-Pro-NHNp by dipeptidyl peptidase IV.

Animals↗
PubMed1987

Synthesis and cloning of a human beta-casomorphin-5 gene.

As so far a singularity among opioid peptides, bovine beta-casomorphin-5 has been shown to display pronounced cardiatic activities. The gene sequence of a human beta-casomorphin-5, including plasmid insertion and fusion protein expression and cleavage instrumentary, has been synthesized by a manual phosphoramidite procedure and cloned in a bacterial system.

Amino Acid Sequence↗